The preparation of styrenic block copolymers is well known in the art. Generally, styrenic block copolymers (“SBC”) can comprise internal polymer blocks and terminal end polymer blocks comprising chemically different monomer types thereby providing particular desirable properties. As an example, in a more common form, SBC's may have internal blocks of conjugated diene and external blocks having aromatic alkenyl arenes. The interaction of the differing properties of the polymer blocks allow for different polymer characteristics to be obtained. For example, the elastomer properties of internal conjugated diene blocks along with the “harder” aromatic alkenyl arenes external blocks together form polymers which are useful for an enormous variety of applications. Such SBC's can be prepared through sequential polymerization and/or through coupling reactions.
It is known also that SBC's can be functionalized in order to further modify their characteristics. An example of this is the addition of sulfonic acid or sulfonate ester functional groups to the polymer backbone. One of the first such sulfonated block copolymers is disclosed, for example, in U.S. Pat. No. 3,577,357 to Winkler. The resulting block copolymer was characterized as having the general configuration A-B-(B-A)1-5, wherein each A is a non-elastomeric sulfonated monovinyl arene polymer block and each B is a substantially saturated elastomeric alpha-olefin polymer block, said block copolymer being sulfonated to an extent sufficient to provide at least 1% by weight of sulfur in the total polymer and up to one sulfonated constituent for each monovinyl arene unit. The sulfonated polymers could be used as such, or could be used in the form of their acid, alkali metal salt, ammonium salt or amine salt. According to Winkler, a polystyrene-hydrogenated polyisoprene-polystyrene triblock copolymer was treated with a sulfonating agent comprising sulfur trioxide/triethyl phosphate in 1,2-dichloroethane. The sulfonated block copolymers were described as having water absorption characteristics that might be useful in water purification membranes and the like, but were later found not to be castable into films (U.S. Pat. No. 5,468,574).
More recently, U.S. Pat. No. 7,737,224 to Willis et al., disclosed the preparation of sulfonated polymer and inter alia illustrated a sulfonated block copolymer that is solid in water comprising at least two polymer end blocks and at least one saturated polymer interior block wherein each end block is a polymer block resistant to sulfonation and at least one interior block is a saturated polymer block susceptible to sulfonation, and wherein at least one interior block is sulfonated to the extent of 10 to 100 mol percent of the sulfonation susceptible monomer in the block. The sulfonated block copolymers are described as being able to transport high amounts of water vapor while at the same time having good dimensional stability and strength in the presence of water, and as being valuable materials for end use applications which call for a combination of good wet strength, good water and proton transport characteristics, good methanol resistance, easy film or membrane formation, barrier properties, control of flexibility and elasticity, adjustable hardness, and thermal/oxidative stability.
Additionally, WO 2008/089332 to Dado et al., discloses a process for preparing sulfonated block copolymers illustrating, e.g., the sulfonation of a precursor block polymer having at least one end block A and at least one interior block B wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation wherein said A and B blocks are substantially free of olefinic unsaturation. The precursor block polymer was reacted with an acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent. According to Dado et al., the process results in a reaction product which comprised micelles of sulfonated polymer and/or other polymer aggregates of definable size and distribution.
It has also been reported that sulfonated polymers may be neutralized with a variety of compounds. U.S. Pat. No. 5,239,010 to Pottick et al., and U.S. Pat. No. 5,516,831 to Balas et al., for example, indicate that styrene blocks with sulfonic acid functional groups may be neutralized by reacting the sulfonated block copolymer with an ionizable metal compound to obtain a metal salt.
Additionally, U.S. Pat. No. 7,737,224 to Willis et al. indicates the at least partial neutralization of sulfonated block copolymers with a variety of base materials including, for example, ionizable metal compounds as well as various amines. More specific amine neutralized sulfonated block copolymers are described in U.S. Pat. No. 2011/0086982 to Willis et al. Membranes comprising these amine neutralized sulfonated block copolymers transport water and are dimensionally stable under wet conditions